This invention relates to devices for the treatment of heart disease and particularly to endo-arterial prostheses, which are commonly called stents. More particularly, the invention relates to catheter assemblies for releasably securing the stent to the catheter during delivery through a body lumen.
Several interventional treatment modalities are presently used for heart disease including balloon and laser angioplasty, atherectomy and by-pass surgery. In typical balloon angioplasty procedures, a guiding catheter having a performed distal tip is percutaneously introduced through the femoral artery into the cardiovascular system of a patient in a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated in the ostium.
A guide wire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guide wire is first advanced out of the distal end of the guiding catheter into the patient""s coronary vasculature until the distal end of the guide wire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy over the previously introduced guide wire until the balloon of the dilatation catheter is properly positioned across the lesion.
Once in position across the lesion, the balloon, which is made of relatively inelastic materials, is inflated to a predetermined size with radiopaque liquid at relatively high pressure (e.g., greater than 4 atmospheres) to press the arteriosclerotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then deflated so that blood flow can be resumed through the dilated artery and the dilatation catheter can be removed therefrom.
Further details of dilatation catheters, guide wires, and devices associated therewith for angioplasty procedures can be found in U.S. Pat. No. 4,323,071 (Simpson-Robert); U.S. Pat. No. 4,439,185 (Lindquist); U.S. Pat. No. 4,516,972 (Samson), U.S. Pat. No. 4,538,622 (Samson, et al.); U.S. Pat. No. 4,554,929 (Samson, et al.); U.S. Pat. No. 4,616,652 (Simpson); U.S. Pat. No. 4,638,805 (Powell); U.S. Pat. No. 4,748,982 (Horzewski, et al.); U.S. Pat. No. 5,507,768 (Lau, et al.); U.S. Pat. No. 5,451,233 (Yock); and U.S. Pat. No. 5,458,651 (Klemm, et al.), which are hereby incorporated herein in their entirety by reference thereto.
One problem which can occur during balloon angioplasty procedures is the formation of intimal flaps which can collapse and occlude the artery when the balloon is deflated at the end of the angioplasty procedure. Another problem characteristic of balloon angioplasty procedures is the large number of patients which are subject to restenosis in the treated artery. In the case of restenosis, the treated artery may again be subjected to balloon angioplasty or to other treatments such as by-pass surgery, if additional balloon angioplasty procedures are not warranted. However, in the event of a partial or total occlusion of a coronary artery after the balloon is deflated, the patient may require immediate medical attention, particularly in the coronary arteries.
A focus of recent development work in the treatment of heart disease has been directed to endoprosthetic devices called stents. Stents are generally cylindrically shaped intravascular devices which are placed within an artery to hold it open. The device can be used to prevent restenosis and to maintain the patency of a blood vessel immediately after intravascular treatments. In some circumstances, they can also be used as the primary treatment device where they are expanded to dilate a stenosis and then left in place.
One method and system developed for delivering stents to desired locations within the patient""s body lumen involves crimping a stent about an expandable member, such as a balloon on the distal end of a catheter, advancing the catheter through the patient""s vascular system until the stent is in the desired location within a blood vessel, and then inflating the expandable member on the catheter to expand the stent within the blood vessel. The expandable member is then deflated and the catheter withdrawn, leaving the expanded stent implanted within the blood vessel, holding open the passageway thereof.
However, retaining the position of the stent in the proper location on the expandable member while advancing the catheter through the body lumen has been found to be difficult. If the stent is dislodged from or moved on the expandable member the system will not correctly deliver the stent into the body lumen. This would require repeating the procedure. This delays insertion of the stent into the body lumen which may adversely affect the patient""s health.
Different methods have been attempted to maintain the position of the stent on the expandable member. One such method involves a protective sheath surrounding the catheter and stent assembly, which is retracted prior to inflation of the expandable member. The use of the sheath, however, increases the profile of the catheter assembly which must traverse narrow vessels. It would be an improvement to use a technique which does not increase the overall profile of the catheter assembly.
Another method has been to remove the friction reducing coating on the expandable member in the location of the stent thereby allowing the catheter assembly""s pre-coated surface to hold the stent in frictional contact. This method has not proven highly efficient in maintaining the stent in the desired location.
Still another method involves application of high pressure to force the inflation balloon into gripping contact with gaps or openings between struts in the stent wall. Should the gaps between stent struts be relatively small, however, such a method may have limitations. Other methods require heat to flow balloon material into the gaps or a balloon coating.
What has been needed is a reliable and convenient means of maintaining a stent in a desired location on a stent delivery system without substantially increasing the overall profile of the catheter assembly. The present invention satisfies this need.
This invention is directed to an improvement in stent delivery systems for releasably securing a stent onto an expandable member of a catheter. The improvement of this invention includes placing deformable material between the outer surface of the expandable member and the stent coaxally disposed thereon. The deformable material is affixed to an expandable member, such as a dilatation balloon and is sufficiently compliant to be deformed by compressive engagement with the stent. The material sandwiched between the expandable member and the stent is compressed projecting a portion of the material adjacent the stent into a physical stop that impedes lateral movement of the stent relative to the balloon during travel to the target site. The deformable material may be an adhesive or a curable compound in a cured or uncured state. The affixed material may be brought into releasably secure contact with the stent by closing the stent inwardly toward, and into engagement with, the underlying expandable member, expanding the expandable member outwardly toward, and into engagement with, the stent, or both. Compressing the stent toward the balloon may include crimping the stent. Once at the target site, the stent is expanded by way of inflation of the expandable member. Any adhesive contact between the stent and the expandable member is broken and the stent is expanded to its implanted diameter. The expandable member is deflated and withdrawn from the patent leaving the stent implanted in a body lumen, such as a coronary artery.
The deformable material is applied to the outer surface of the balloon followed by the coaxial mounting of the stent thereover. In the adhesive form, the deformable material can be applied in a thin layer over selected portions of the balloon surface to provide, upon crimping of the stent, inflation of the balloon, or both, adhesive engagement with the stent. Deformable material may be applied, whether adhesive or otherwise, to the balloon so that as the material becomes compressed it forms physical stops adjacent to stent struts, the stops serving to block longitudinal movement of the stent relative to the expandable member. Deformable material may also be applied in sufficient thickness, up to the thickness of the stent wall, to form a continuous smooth outer surface of the distal portion of the assembly without substantially increasing the insertion profile of the stent.
Affixed to the outer surface of a dilatation balloon, the unexpanded stent is transported as part of the catheter assembly through the vessel pathway to the desired stenotic site. Once at the site, the balloon is inflated transferring circumferential expansion force to the expandable stent. Subjected to such force from the balloon, the stent is expanded against the vessel wall to the desired configuration. The balloon is then deflated, unsecured from the expanded stent, and withdrawn leaving the expanded stent to support the vessel wall.
Should the stent become adhered to the material, the expansion and contraction forces imparted by the balloon to the material serve to dislodge the material from the stent. If the deformable material is an adhesive and is at least substantially tacky at the time of contact with the stent, it is preferable that the deformable material have greater affinity for the balloon than to the stent so that the material remains affixed to the balloon upon deflation and withdrawal of the balloon.
Preference for adherence of the material to the balloon is provided in a number of ways. For example, the composition of the outer surface of the balloon and the inner surface of the stent may differ so that the material adheres more strongly to the expandable member. Silastic rubber and Nylon, for example, are often used as balloon material. Adhesion to such materials are typically greater than, for example, stainless steel, a widely used stent material. Additionally, adhesive may be formulated to covalently bond to the balloon material which is often made from polyethylene (PE), polyethylene terephthalate (PET), or Nylon.
If adherence properties of the stent and balloon surfaces are not substantially different, a curable adhesive, for example, may be utilized so that affixation to the balloon occurs when adhering properties of the adhesive are greater when applied to the balloon than when later compressively or adhesively engaged to the stent. After curing, the adhering properties of the adhesive are decreased, so that the stent may be crimped over the material resulting in a weaker interface between the stent surface and the adhesive than to the balloon surface and the adhesive. The adhesive should be applied so that it separates from the stent no later than at maximum deflation of the expandable member at the implant site.
The degree of tackiness or stickiness of the adhesive of the present invention may be chosen from a variety of deformable materials such as polymers, urethanes, and adhesives of varying adhesive strengths as desired. Adhesive may be chosen in consideration of a number of factors including, but not limited to, the rigors and forces expected to be encountered by the stent and the expandable member during travel to the stenotic site, the extent of frictional resistance provided by the mounting and crimping of the stent onto the expandable member, and the extent of separation force made available by the inflation and deflation of the expandable member. After the deformable adhesive is applied, the stent is positioned over the adhesive and is tightly crimped, and/or the balloon is expanded, into compressing and/or adhesive engagement with the adhesive.
The balloon is preferably folded prior to application of the material in typical S or tripartate propeller fashion exposing balloon wing edges. In one embodiment, the deformable material is applied to the wing edges. Application of the material to the interior of the balloon folds is preferably avoided so that the folded wings of the balloon do not stick together thereby inhibiting expansion and so that the material does not cause unnecessary buildup of the insertion profile of the assembly.
The deformable material, whether in the form of an adhesive or otherwise, may be applied sparingly so that the folded profile of the balloon is not increased substantially and so that the stent is easily separated from the balloon when the balloon is inflated and deflated. Sparse application may be as small as a dot or drop of deformable material not exceeding a thickness of 0.01 centimeter, for example, or may be, in another example, a bead of deformable material placed longitudinally along or circumferentially radially about the outer surface of the balloon. The thickness of the dot or drop or bead of deformable material can range from about 0.001 to 0.01 cm, but may be larger or smaller depending upon the application.
The material may be cured or uncured prior to engagement with the stent. By way of example, nine drops of UV curable Dymax polyurethane can be applied sparingly to a tripartite balloon, three drops along each of the three folded wing edges at the proximal, middle, and distal sections of the balloon. The polyurethane can be fully cured prior to crimping to provide a very soft, flexible, and somewhat sticky or tacky surface. The stent thereafter can be positioned coaxially over the cured material and crimped tightly to compress the material to form one or more physical stops adjacent one or more stent struts.
Compression of at least some of the material beneath the stent struts may serve to force the deformable material into one or more gaps adjacent the struts and/or adjacent one or more end struts. The material formed adjacent the struts forms physical stops blocking movement of the stent relative to the balloon during travel to the stenotic site. If the material is sufficiently thick it may also contact the wall surfaces of the stent struts defining the depth of the gaps and may thereby provide, upon cure, additional adhesion and/or frictional contact with the stent before stent expansion.
The depth of the deformable material, whether in the gaps, beneath the stent struts, or otherwise, may be controlled. A smooth outer stent surface may be achieved by compressing the struts in sufficient deformable material. However, so that the insertion profile of the catheter assembly is not substantially increased, the deformable material should not exceed the thickness of the stent. The thickness of the stent can vary widely as is known in the art. Typical stent thicknesses range from about 0.0015 to about 0.050 inch (0.0381 to 1.27 mm), but can vary considerably from these dimensions depending upon a particular application, such as use in coronary or peripheral vessels. Additionally, care must be taken not to submerge the stent struts into the material to such an extent that expansion of the stent and detachment of the stent from the expandable member is prevented. Manufacture of the assembly may be under standard atmospheric pressure, humidity, and at room temperature. Application of extraneous heat is unecessary.
After travel to the stenotic site in the unexpanded state, the radial circumference of the balloon is increased by inflation. With expansion of the outer surface of the balloon, the stops formed adjacent the stent struts move outwardly and away from one another and away from the struts of the expanding stent to form proximal gaps between the struts and the stops. The movement of the stops away from the struts increases the freedom of movement of the struts and enhances disengagement of the expandable member from the stent upon deflation.
In lieu of, or in addition to crimping, the deformable material affixed to the balloon may be shifted into compressing engagement with the stent by way of inflation of the balloon toward the stent. During manufacture, a containing device, such as a sheath, should be placed over the stent to prevent premature expansion and to maintain the stent in a low insertion profile. However, the stent may be unconstrained if the deformable material is sufficiently pliable to be compressed by the stent without causing expansion of the stent. Uncured polyurethane or polymeric foam, for example, is such a sufficiently pliable material.
The invention can be used with the known configurations of stent delivery systems including, for example, over-the-wire (OTW) intravascular catheters, monorail catheters, and rapid exchange (Rx) intravascular catheters.